The present invention relates to a silver halide photographic material.
Silver halide color photographic materials, particularly silver halide photographic materials for photographing use, has always been desired to be highly sensitive and excellent in the image quality. Particularly, with the recent popularlization of portable miniature cameras in the photographic field, even a small-size negative has become demanded to give an image comparable in the quality with that from a large-size negative. So to speak, there has been a strong demand for the development of a silver halide color photographic material whose resolution as well as sharpness is not degraded even in a large magnification.
Various techniques have been conventionally known for improving the sharpness. One of the techniques is for the improvement of the edge effect, and another is for the prevention of light scattering. Examples of the edge effect improving technique include the method using an unsharp mask in the printing field and the method using a DIR coupler for color negative film. Of these the method using an unsharp mask has its limit of practical use because its process is complex. There are many known methods using DIR couplers; useful examples of the DIR coupler include those compounds as described in Japanese Patent Examined Publication Nos. 34933/1980, Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No. 93344/1982, U.S. Pat. Nos. 3,227,554, 3,615,506, 3,617,291, 3,701,783, and the like. However, where a DIR coupler is used to stress the edge effect, the MTF (modulation transfer function), although it is improved in a lower-frequency region, cannot be expected to be improved in a higher-frequency region required necessary for a high magnification, and is accompanied by an adverse side effect such as the deterioration of sensitivity or of density. If a DIR coupler capable of extending its affect away such as a diffusible DIR or timing DIR coupler is used, the deterioration of sensitivity or density could be lessened, but the improvement is no more than a shift of the MTF toward the lower frequency side, and no high magnification cannot be expected.
On the other hand, those known as the technique for preventing light scattering include the method for coarsening silver halide emulsion grains, the method of adding a coloring material, the method of reducing the layer thickness, and the like.
The first-mentioned method is known for improving the image sharpness by coarsening the grain size of silver halide grains up to the degree where light scattering is minimized. This technique, however, has the disadvantage that the coarsened grains give a visual impression of the deterioration of graininess. The second method is an attempt to improve the image sharpness by the addition of a coloring material, known examples of which include the method for coating an antihalation layer as described in West German OLS Patent No. 2711220, and the method of incorporating a filter dye into a protective layer as described in Japanese Patent O.P.I. Publication No. 161235/1980. These techniques, however, are disadvantageous in respect of decreasing the photographic speed, throwing out of the color balance, increasing fog, etc. of a photographic material. Known as the third method for reducing the layer thickness is the method of largely reducing the coating amount of silver. However, if the coating amount of silver is largely reduced, then the active site is reduced, thereby inviting the deterioration of grainness. The reduction of the layer thickness is also carried out by reducing the gelatin, coupler or coupler solvent in a coating liquid. However, any of these methods is undesirable in respect of inviting the deterioration of the coatability or density of the color formed.